1. Technical Field
The present disclosure relates to a millimeter-wave communication control method and a millimeter-wave communication control apparatus.
2. Description of the Related Art
In recent years, with respect to a sharp increase in traffic demand, a study has been conducted on adoption of small-size base-station apparatuses that perform communication using a millimeter-wave band in order to obtain a bandwidth of 1 GHz or more. One example of implementation is a communication system (which may also be referred to as a “heterogeneous network”) in which a plurality of small-size base-station apparatuses are provided in a communication area of a base-station apparatus that performs communication using a microwave band.
Since the small-size base-station apparatuses use a millimeter-wave band, the propagation loss increases. Consequently, it is difficult to increase the distance the radio wave reaches.
One method that contributes to an improvement in such propagation loss, an increase in the communication speed, and an increase in the cell area (the communication area) is a method in which a base-station apparatus performs directivity control (beamforming) by using a plurality of antenna elements (an antenna array). With the method that performs directivity control, it is possible to make the radio wave to reach a greater distance than the distance the radio wave of omnidirectional transmission reaches, by directing the radio wave to be transmitted by the base-station apparatus in the direction in which a terminal (a “terminal station apparatus” or a “station (STA)”) is located (i.e., by using directivity). Thus, the method that performs directivity control can increase the cell area covered by the base-station apparatus. Also, the Signal to Interference-plus-Noise power Ratio (SINR) of the terminal can be improved. Since the method makes it possible to apply a modulation scheme and a coding rate which provide a high spectrum use efficiency, communication can be performed at high transmission speed (see, for example, IEEE 802.11ad-2012 Standard for Information Technology-Telecommunications and Information Exchange between systems-Local and Metropolitan networks-Specific requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 3: Enhancements for Very High Throughput in the 60 GHz Band).
In a heterogeneous network, wireless resources of a millimeter-wave network including a plurality of small-size base-station apparatuses may be secondarily used by a terminal in another system, and such an approach is also effective. For example, when a terminal that supports both a microwave network and a millimeter-wave network is using the microwave network, the terminal may be permitted to secondarily use the wireless resources of the millimeter-wave network. However, in the related art, when the wireless resources of the millimeter-wave network are secondarily used by a terminal belonging to another network, it takes time to establish an initial connection.